1. Field of the Invention
This invention pertains to the determination of total carbon in liquid samples.
2. State of the Prior Art
In an article by M. Ehrhardt entitled "A New Method for the Automatic Measurement of Dissolved Organic Carbon in Sea Water" published in Deep-Sea Research, Vol. 16, pages 393-397 (1969), a technique is described for determining total organic carbon in a seawater sample by oxidizing dissolved organic matter in the sample with potassium peroxidisulfate as an oxidizing agent, using ultraviolet radiation to promote the oxidation. Carbon dioxide produced by oxidation of the organic matter is then measured for total carbon by conductometric means.
An article by P. D. Goulden and T. Brookbank entitled "Automated Determinations of Dissolved Organic Carbon in Lake Water" published in Analytical Chemistry, Vol. 47, pages 1943-1946 (1975) discusses a similar technique for determining total organic carbon in an aqueous sample. This article describes use of persulfate ion as an oxidizing agent in an ultraviolet-promoted oxidation reaction, and use of infrared detection means to measure total carbon in carbon dioxide produced by oxidation of the organic matter.
P. Wolfel and H. Sontheimer, in an article entitled "Ein neues Verfahren zur Bestimmung von organisch gebundenem Kohlenstoff im Wasser durch photochemische Oxidation" published in Vom Wasser, Vol. 43, pages 315-325 (1974), describes a technique for determining total organic carbon dissolved in an aqueous sample by exposing the sample to ultraviolet radiation from a low-pressure mercury vapor lamp immersed in the sample in order to oxidize organic matter in the sample to carbon dioxide, and then using infrared detection means to measure the carbon dioxide so produced. Immersion of the mercury vapor lamp in the sample enables the ultraviolet energy from the lamp to enter the sample directly after passing through the lamp envelope, thereby maximizing the energy available for oxidizing organic matter in the sample.
In U.S. Pat. No. 3,958,941 granted on an invention by M. Regan, a technique for determining total organic carbon in an aqueous sample is described in which air and water are circulated through an irradiation chamber having an ultraviolet lamp mounted therein. Separate air circulation and water circulation systems are provided, but both systems share a common flowline leading into the irradiation chamber. A sample to be analyzed for total carbon is injected into the common flowline, and is conveyed by the circulating water into the irradiation chamber wherein organic carbon in the sample is oxidized to carbon dioxide by radiation from the ultraviolet lamp. The air circulating through the irradiation chamber sparges carbon dioxide generated by the oxidation process from the chamber, and conveys the carbon dioxide to a conductometric device for determining total carbon.
Oxidation of dissolved carbonaceous matter in a liquid sample using ultraviolet radiation and an oxidizing agent to promote the oxidation process was known in the prior art. Nevertheless, attempts to automate the oxidation of carbonaceous matter in a plurality of discrete liquid samples in succession using ultraviolet radiation and an oxidizing agent encountered difficulties that were not overcome until the present invention.
When successive liquid samples are introduced into a reactor for oxidation of carbonaceous matter dissolved therein by an oxidizing agent and ultraviolet energy, complete oxidation of the carbonaceous matter in each successive sample cannot be assured unless the supply of oxidizing agent in the reactor is continuously replenished so as to provide sufficient oxidizing agent for each successive sample. Until the present invention, no technique was known for assuring that an adequate supply of oxidizing agent could be provided for each successive sample introduced into a reactor for total carbon analysis.